Flowers exhibit remarkable variation in form, affecting how pollinating insects recognize them, but the evolution of that form is not well understood. The mints and their relatives are a good group in which to study the evolution of floral shape, because there have been many changes from radial symmetry to bilateral symmetry and back. This project will test the hypothesis that (a) a major shift from radial symmetry to bilateral symmetry within the mint relatives correlates with extra copies of floral symmetry patterning genes, and changes in gene expression; (b) a return to radial symmetry occurred by diversification of the same genes.
Mints and their relatives are commonly used as ornamental plants for their spectacular flowers; they will thus provide an excellent backyard example for the education of the general public on evolution and development, and plant-insect interactions. Additionally, the project will involve the training of two undergraduate students.
Flowers exhibit remarkable variation in form and display, which can affect how pollinating insects recognize them. We do not understand much about how floral shapes have evolved. The mints (Lamiaceae) and their relatives are a good group in which to study floral shape, because there have been many changes from radial symmetry to bilateral symmetry and back. In addition, the number of stamens changes in evolutionary time. We hypothesize that (a) a major shift from radial symmetry to bilateral symmetry within the mint relatives correlates with extra copies of floral symmetry patterning genes, and changes in gene expression; (b) a return to radial symmetry occurred by diversification of the same genes. To test these hypotheses, we combine gene expression and developmental data and infer the history of the floral patterning genes to explain the diversity and evolution of floral form within the mint relatives. This project found that asymmetrical expression of of floral symmetry CYC2-like genes but not their duplication is correlated with the origin of bilaterally symmetrical flowers. We also found evidence for distinct evolutionary developmental mechanisms underlying derived radially symmetrical flowers. Additionally, we found that the interactions of floral symmetry patterning genes might have evolved in a stepwise fashion. Mints and their relatives are commonly used as ornamental plants for their spectacular flowers; they thus provide an excellent backyard example for the education of the general public on evolution and development, and on plant-insect interactions. Two undergraduate students at UM-St. Louis were involved in this project and helped with DNA work and microscopy. Results from this study were presented at various scientific conferences and were published in peer-reviewed journals.
